1. Field of the Invention
The present invention relates to a shift control device provided to a shift operation unit including a shift lever which automatically returns to a predetermined home position.
2. Description of the Related Arts
A vehicle which includes an automatic transmission as a transmission is provided with a shift operation unit by which the state of the transmission such as Driving (D), Reverse (D), and Neutral (N) is set in the automatic transmission. Some shift operation unit is configured such that a shift lever is automatically returned to a predetermined position (Home position) when a driver releases the shift lever after setting the state of the automatic transmission by operating the shift lever.
In such a shift operation unit, a plurality of shift positions corresponding to the states of the automatic transmission is provided on a path (shift pattern) on which the shift lever is moved. Further, the shift operation unit is configured such that when the shift lever is positioned in one of the shift positions, a shift position signal which notifies the position of the shift lever is input to a shift control device which controls the automatic transmission. The shift control device is configured such that the state of the automatic transmission is set in accordance with the input shift position signal.
A shift position corresponding to the sate of Driving (D), a shift position corresponding to the state of Reverse (D) and a shift position corresponding to the state of Neutral are respectively referred to as a D position, an R position and an N position, hereinafter. A shift position to which the shift lever is automatically returned is referred to as an H position (home position).
Although the arrangement of the shift positions is not limited, the N position which sets the automatic transmission in the Neutral state is preferably arranged in a position to which the shift lever can be directly moved from the D position, the R position and the H position in consideration of operability and convenience. Thus, a shift pattern is preferable which is made by combining a path directly connecting the N position and the D position, a path directly connecting the N position and the R position and a path directly connecting the N position and the H position. In such a shift pattern, the shift lever inevitably passes through the N position when the driver moves the shift lever to the D position or the R position from the H position. Similarly, the shift lever inevitably passes through the N position when the shift lever automatically returns from the D position or the R position to the H position (during automatic return).
If the shift control device detects that the N position is selected when the shift lever passes through the N position during the automatic return to the H position, the automatic transmission is mistakenly set to be the Neutral state during the automatic return of the shift lever.
In order to solve the problem, Unexamined Japanese Patent Application Publication No. 2005-007993 discloses a shift operation device in which a time period (recognition time period) required for the shift control ECU (shift control device) to detect the selection of the neutral position when the shift lever is positioned in the neutral position (the N position) is set longer than the recognition time period of the other shift positions.
The shift operation device (shift operation unit) disclosed in Unexamined Japanese Patent Application Publication No. 2005-007993 is configured such that the shift control ECU detects the selection of the shift position in which the shift lever is positioned when the shift lever has been held in the shift position for a time period longer than the recognition time period set for the shift position.
Since the recognition time set for the neutral position is longer than those of the other shift positions, it is possible to prevent the shift control ECU from wrongly detecting the selection of the neutral position by the shift lever when the shift lever passes through the neutral position during automatic return to the Home position.
However, due to the deterioration of the shift operation device caused by the time degradation (endurance deterioration), the moving speed (returning speed) in which the shift lever automatically returns to the Home position may become lower. If the returning speed becomes lower, the shift control ECU may determine that the shift lever has been held in the neutral position longer than the recognition time period when the shift lever automatically returning to the Home position passes through the neutral position. In this case, the shift control ECU wrongly detects that the shift lever selects the neutral position when the shift lever automatically returning to the Home position passes through the Neutral position. In order to prevent the wrong detection, the recognition time period set for the neutral position needs to be long enough.
In a configuration that the shift control device detects the failure of the shift operation device when a shift position signal notifying a shift position is continuously input to the shift control device longer than a predetermined recognition time period, when the degradation of the shift operation device is worse and the returning speed of the shift lever becomes lower, a shift position signal has been output longer than the predetermined recognition time period when the shift lever passes through the Neutral position during the automatic return. Thus, there is a disadvantage that the shift control device may wrongly detect that the shift operation device has a failure. In the shift control device configured as described above, it is preferable that the recognition time period set for the neutral position is set long enough in order to prevent the wrong detection.
In the shift operation device configured as described above, the recognition time period set for the neutral position is set longer than the recognition time period which is suitable when the deterioration degree of the shift operation device is low. Therefore, there is a problem that the shift lever needs to be held in the neutral position over a long time for setting the automatic transmission in the neutral state even when the deterioration degree of the shift operation device is low. This decreases the operability of the shift operation device.